Muscular strengthening device



FIG. 1 is a right elevation view of a muscular strengthening device showing my new design, the opposite side being a mirror image of the shown;

FIG. 2 is a front elevation view thereof;

FIG. 3 is a rear elevation view thereof;

FIG. 4 is a top plan view thereof;

FIG. 5 is a bottom plan view thereof; and,

FIG. 6 is an isometric view thereof. 

The ornamental design for a muscular strengthening device, as shown and described. 